Plug valves employed for the control of fluids through conduits such as pipelines and the like comprise a valve body having two or more ports with associated pipe joint connectors and an internal control plug. The plug is rotatable between several positions in order to shutoff or permit the flow of fluid through the valve. The valve plugs may be of a generally spherical shape as in the case of so called "ball valves" or they may be of cylindrical or tapered configuration. Such valves may be in-line valves in which the outlet and inlet ports are generally diametrically opposed relative to one another or they may be angle type valves in which the inlet and outlet ports are angularly disposed, normally at an angle of 90.degree., with respect to one another.
A common expedient in plug valves is to encase the valve plug in one or more resilient seat members positioned within the barrel of the valve casing. For example, U.S. Pat. No. 3,192,948 to Anderson et al discloses in-line and angle-type ball valves in which a generally spherical valve member is mounted within a conforming seat member formed of a resilient materials such as polyethylene halides, e.g. teflon, polyamides or nylons. The seat member is sufficiently deformable to accommodate minor surface irregularities. The spherical valve member includes an integral stem which extends upwardly through openings in the seat member and the surrounding cage structure to the exterior of the valve. A bonnet having an aperture through which the valve member stem extends closes the upper opening of the valve cage and covers a resilient pressure acting stem seal.
U.S. Pat. No. 3,735,956 to Matousek discloses a three-way angle ball valve in which a generally spherical valve plug is mounted within the valve body on articulated packing material formed in two pieces of a resilient plastic material. The packing sections, when fitted together, form openings aligned with the control ports in the valve body and have cylindrical recess sections which leave a lip of packing material adjacent the ball member. Metal ring members are mounted within the packing material recesses to maintain the lips in engagement with the surface of the ball member.
Another valve configuration employing an in-line ball valve in which a flow control element is disposed between inlet and outlet ports and supported on resilient seat members as disclosed in U.S. Pat. No. 4,552,335 to Alexander et al. In Alexander, the seat members include an internal core member, an annular metal reinforcing ring for the core member, and face body and rear body seals formed of an elastomeric material such as neoprene. The ball element is said to float within the valve housing and is not directly connected to a drive trunnion so that it can seek its own position relative to the downstream seat to provide improved sealing action. The seats and floating ball member are held in place within the valve body by means of a threaded end cap which is provided with an O-ring seal between the valve barrel and the end cap.
In addition to forming valve seats of resilient materials, plug-type valves can also employ control members formed of such materials. Thus, U.S. Pat. No. 2,967,042 to Richter discloses an angle-type shutoff valve in which a tapered plug member is rotatably mounted within a valve body against a conforming tapered sealing ring. Both the valve plug member and the tapered sealing ring are formed of a plastic material such as high density polyethylene which has a slight resiliency.
U.S. Pat. No. 3,940,107 to Allenbaugh discloses an in-line ball valve structure in which a ball member is rotatably mounted on a lower pivot pin threadedly secured in the valve housing and is actuated by a diametrically opposed upper drive trunnion. The inlet and outlet ports in the valve body are provided with annular seal elements formed of a synthetic resin. Each seal resin is provided with an opening defined by a conically divergent lip portion which seats on the spherical surface of the ball element.